Shedding Some Light on Circadian Evolutionary Mismatches
Or how being cool might decrease the impacts of age on your circadian system
The idea that the spaces we occupy and use within our built environments might be “mismatched” to varying degrees with intended uses, actual uses, and health and productivity needs isn’t new. These mismatches result from a variety of factors, including compromises made during planning, design, and construction, an inadequate understanding of how to account for relevant physiological, psychological, and social/cultural factors, inadequate engagement of key stakeholders, as well as disciplinary/team silos. The needs of the organization and/or individuals using the space(s) may also evolve beyond a building’s capabilities post occupancy.
The building/occupant organism is complex (see Figure 1 below), making it fairly easy for some degree of mismatch to occur. There are the individual occupants, or people, with their own physiological and psychological needs. There are the organizations housed within the facility, made up of individual occupants, and subject to their own policies and cultural norms, in varying degrees of alignment with the cultural norms of the larger encompassing communities and society.
There are the environments that shape, constrain, facilitate, or hamper the desired actions of the individuals and organizations occupying the facility. These environments are both the physical building itself and the social/cultural environment, which consists of the various organizational cultural norms present, as well as those of the larger encompassing communities and society.
Together these make up the building/occupant organism (or ecosystem). But the design, construction, and operation of this organism occurs within a larger nested hierarchy of groups up to the global level, each with varying needs and goals, in varying degrees of alignment and conflict. The interaction of this organism within the context of these nested hierarchies impacts its performance, further impacting the health, wellness, and productivity of all involved.
Mismatches are difficult to avoid if we don’t mindfully take this level of complexity into account (making it more difficult than matching black and navy socks in the dark). Finding, understanding, and addressing such mismatches are also why we need post occupancy evaluations and continuous monitoring, but that’s another story.
In this post I’m going to focus on one specific category of mismatches - evolutionary mismatches - that result from inadequately taking our evolutionary history into account. That history, spent primarily in small groups and in physical environments vastly different from our contemporary indoor environments, also shapes and constrains what the optimal configuration of the building/occupant organism should be.
Evolutionary mismatches are basically occurrences where an organism’s traits or systems (like our circadian system) that were adaptable in an “ancestral” environment end up being less adaptive or even maladaptive in another environment different from the one they evolved within. Evolutionary mismatches can negatively impact our health and wellness as well as our productivity. This View of Life Magazine previously published a a series of articles on evolutionary mismatches worth reviewing, starting with the following introductory piece: Evolutionary Mismatch and What To Do About It. Prosocial.world also produced an informative video series based on many of these articles: Evolutionary Mismatch and What to Do About It.
Speaking of the circadian system, it’s a good example to use for discussing the concept of evolutionary mismatch in more detail. Let’s start with a basic, high level description of what our circadian system is. You can refer to any of the links below for more detailed overviews.
Our circadian clock (Figure 3) refers to an approximate 24-hour cycle of physiological activity that our bodies go through every day. Circadian photoentrainment is the process of using light to “entrain” our bodies to a specifically-timed cycle, where light synchronizes our biology with the external world. And our eyes are the windows this exterior light signal passes through to reach our clock.
We’re day-active animals, so our clock is evolutionarily designed to promote wakefulness during the day and sleep at night. The hormone melatonin is an important component of our circadian system, as its production starting in the evening, cued by receding daylight and approaching darkness, is one of the signals our brain uses to “know” it’s time to wind down and hit the hay. And in the morning, enhanced by the presence of light, melatonin secretion stops, thereby signaling our brain to get on with the day.
However, our modern built environments and lifestyles, along with artificial illumination levels often too low during waking hours and excessive during sleeping hours, do not adequately mimic the exterior day/night cycle our circadian system evolved to effectively function in. They create an evolutionary mismatch that limits the amount and quality of our sleep, negatively impacting our health and cognitive performance.
It also gets complicated teasing out the intricacies of such mismatches and how to address them. Because we’re talking about the interplay of physiological, psychological, and social/cultural factors in various environmental contexts (recall Figure 1). And the fact that environmental contexts have varying degrees of alignment with our relevant sets of traits and systems only further complicates this.
One way to tease out these complex intricacies is to use biologist Nikolaas Tinbergen's four characterizations of traits – function, mechanisms, development, and heritable history. Breaking traits, or systems of traits, down into these four characterizations can paint a clearer picture of how our evolutionary history, including past environments, shaped them to optimally function. It can provide greater insight into how various technologies or contemporary environmental conditions could negatively impact this functioning and our health.
So let’s examine our circadian system using these four trait characterizations. Starting with Function, this refers to the ultimate reason for the system’s evolution. In this case it was to help regulate the human biological clock.
The Mechanisms of the circadian system refer to how it physically works in humans – how the patterns of light and dark that reach the back of the eyes are converted to neural signals that help synchronize our “biological clocks” with the local time.
The Development of the circadian system over the course of an organism’s lifetime may indicate that it operates differently at different stages of human development or is impacted by the environment differently. Specific cues that evolved in the ancestral environment may actually impact how it develops and how successfully it operates in the new environment.
And finally, its Heritable History refers to how the circadian system evolved over the history of our species, and our species’ ancestors, and how that evolution compares to the evolution of similar systems in other species.
Framing specific traits or a system of traits using these four characterizations allows us to develop some targeted questions to help evaluate whether or not environmental conditions, design strategies, the use of certain technologies, etc., might create an evolutionary mismatch for humans in general or specific demographic groups. Lets focus on development to demonstrate this.
As noted above, development occurs from conception through death (Figure 4). And different stages of development impact how the mechanisms of the circadian system function, including how efficiently they function. Research does indicate that the circadian system functions less efficiently as we age and is more sensitive to associated environmental mismatches.
For example, as we age there is reduced light transmission through the eye caused by reduced pupil diameter and yellowing of the lens, which hinders light entry for rhythm synchronization. For older adults, this just exacerbates the mismatch of limited access to exterior day/night patterns already created by our modern built environments and lifestyles.
Across the development spectrum, we have a tendency to pay less attention to either end. It’s arguable that both ends have less of a voice, both in general and with respect to the design process in the AEC Industry. As a result, these age ranges tend to be subjected to a greater number of evolutionary mismatches and/or more severe impacts from evolutionary mismatches.
So, referring to Figure 6, one question a designer might ask relative to an assisted living facility is how the varying lives of the facility’s occupants and relevant social/cultural factors at play impact the development and current functioning of their circadian systems. Based on what we know about the circadian system so far, the functioning of our eyes over the course of our lives would be important to consider here.
Sunglasses are certainly a cultural trait, impacting who wears them and how often. They’re reflective of fashion and popular culture and they signal group membership as well as various social and economic statuses. On the small and big screen, as well as in social media, sunglasses both reflect and help define certain cultural conceptions of what cool is.
As well as in the comics.
But sunglasses also function as eye protection. If you wear the right kind of protective eyewear, with lenses that block UVA and UVB light, you limit the damage UV radiation does to your lenses over time, which also decreases the extent of yellowing and the risk of developing cataracts. And less damage to our lenses means increased eye functionality relative to optimizing our circadian system, holding everything else equal.
So, if you’re designing for an older adult population with variation in the amount of sunglass wearing they did over the course of their life (or the quality of the sunglasses they wore), this will likely add to the variation in the functioning of their circadian systems that exists within that population. At the same time, for those individuals who already have eyes less efficient at transmitting light, wearing sunglasses will exacerbate that issue.
This variation could also increase if some individuals have had cataract removal and lens replacement done. As such procedures increase the lens’ spectral transmission, they positively impact the circadian system’s functioning. There are studies (see links above) that show this minimizes the adverse age-related effects on circadian rhythms, cognition, and sleep.
From a design standpoint, lighting systems (alone or in conjunction with daylight) for older individuals in general need to be capable of providing enough illumination to compensate for the reduced light transmittance through their eyes resulting from the effects of aging (and a lifetime of UV exposure). To achieve an equivalent circadian photoreception performance, some research suggests a 65-year-old needs about three times the illuminance of a 25-year-old and about half that of a 85-year-old. And for assisted living centers, the lighting system should be flexible enough to accommodate any potential variation in how efficient the population’s eyes and circadian systems might be functioning as a result of varying life experiences (including sunglass wearing).
The operation of the circadian system is obviously more complex that what I’ve laid out here (refer to the links above for more detailed overviews). We still have things to learn about its how and why. And the lighting community is not in agreement on the best relevant metrics to use, nor how to design for optimal circadian system operation in different contexts and for different demographics. But at a high level this should demonstrate the utility of an evolutionary mismatch framework.
Because understanding the development of the circadian system from conception to death, how that impacts it’s functioning mechanisms, shaped by our evolutionary history as well as the social/cultural factors influencing the lives of individuals, provides important insights for avoiding evolutionary mismatches. And making use of an evolutionary mismatch framework could help answer some of the outstanding questions referred to above.
For example, research suggests that optimal circadian lighting design should consider spectrum (color), lighting levels, timing, duration of exposure, and photic history (previous light exposures). But what would the optimal combination(s) of these five factors be for different demographic groups and different settings? A useful starting point might be to establish what the “baseline” or various ancestral conditions were for our ancestors at the various key stages of the circadian system’s evolutionary development.
From there, one could look at how the manifestations of these five factors in contemporary designed settings differs from their likely manifestations in our relevant ancestral environments. Being aware of these deltas and their potential impacts on the performance of our circadian systems might provide additional insights in interpreting the results of existing research, help formulate new questions and associated research, and suggest other optimal configurations of these five factors in contemporary environments.
Or evaluate alternative optimal configurations already proposed. It’s been suggested that our afternoon post lunch grogginess could be addressed by providing a red luminous panel in our field of view - increasing alertness via the increased lighting intensity at the red end of the spectrum (a caffeinated drink alternative) while avoiding the impact on melatonin suppression resulting from exposure to intense illumination at the blue end of the spectrum. That seems logical based on what we know, but is there anything else about the manifestations of these five factors in our relevant ancestral environments that would support or refute such a set up as part of an optimal, changing configuration of factors over the course of the day?
To wrap things up, at a high level, the process of assessing if a technology, design strategy, or operational policy creates an evolutionary mismatch consists of the following. First, pick a key human system or set of traits likely impacted by the technology, strategy, or policy under consideration and describe it using Tinbergen's four characterizations of traits. Then assess how the real world environments created by the technology, strategy, or policy (taking the complexities of Figure 1 into account) varies from the relevant ancestral conditions that were key to shaping the system or set of traits in question.
As other specialists are required to help determine the nature of the relevant ancestral environments, you may initially need to use contemporary exterior environments as a proxy for the relevant ancestral conditions. Next, develop a set of research questions or hypotheses focused on how the deltas might be impacting system or trait performance. Review the existing scientific literature, engage the relevant third party experts, and talk to the manufacturer to see what supporting or refuting evidence exists for these hypotheses.
At this point designers will have to weigh potential or confirmed benefits of the technology, strategy, or policy versus what the evolutionary mismatch analysis says so far about potential health and productivity risks. It may mean additional research is needed to fully understand whether or not evolutionary mismatches are created for the occupants in question, and if so, the severity of the health and productivity impacts experienced. Designers, facility operators, and building owners should not be afraid to invoke the precautionary principle when warranted.
And you’ll look cooler doing it while donning a pair of shades.